Method for forming positive patterned resist layer on tantalum substrate utilizing quinone diazide composition with aromatic hydroxy additive

ABSTRACT

Proposed is an alkali-soluble, positive-working photosensitive resin composition which can be used as a material for forming a finely patterned resist layer on the surface of a metallic substrate such as tantalum to exhibit excellent adhesion of the patterned resist layer to the substrate surface. The composition comprises, in addition to a novolac resin as a film-forming agent and a naphthoquinone diazide group-containing compound as a photosensitizer, an aromatic compound having two benzene rings and at least five phenolic hydroxy groups in a molecule such as pentahydroxy and hexahydroxy benzophenone compounds as an adhesion improver.

This application is a continuation application of application Ser. No.08/046,239 filed Apr. 13, 1993, now abandoned.

BACKGROUND OF THE INVENTION

The present invention relates to a method for forming a patterned resistlayer on a metallic substrate surface or, more particularly, to a methodfor forming a patterned resist layer on the surface of a substrate ofwhich at least the surface layer is made from a metal such as tantalumwith greatly improved adhesion between the resist layer and the metallicsurface.

It is a well established technology in the manufacture of various kindsof semiconductor devices such as ICs and LSIs and liquid crystal displayunits that the surface of a metallic substrate of aluminum, tantalum,molybdenum, chromium and the like is finely worked by the etching methodin which a thin layer of a photosensitive resin composition is formed onthe substrate surface as a resist layer which is patterned by thephotolithographic process by first exposing the resist layerpattern-wise to actinic rays such as ultraviolet light through apatterned photomask to form a latent image which is developed with adeveloper solution to give a patterned resist layer to be used as aresist in the etching of the metallic substrate surface with an etchingsolution. Various types of photosensitive resin compositions are knownin the prior art to be suitable for the above mentioned purpose, ofwhich those quite satisfactory include positive-working photosensitiveresin compositions comprising an alkali-soluble novolac resin as afilm-forming ingredient and a quinone diazide group-containing organiccompound or, in particular, a quinone diazide group-containingbenzophenone compound as a photosensitive ingredient (see, for example,U.S. Pat. No. 4,377,631 and Japanese Patent Kokai 62-35349, 1-142548 and1-179147).

In the photolithographic etching process of a metallic substrate surfacein the manufacture of semiconductor devices and liquid crystal displayunits, one of the requirements for the photoresist composition is thatthe adhesion between the patterned resist layer and the metallicsubstrate surface is very firm while none of the photosensitive resincompositions of the above mentioned type is quite satisfactory in thisregard, especially, when the substrate has a surface of tantalumalthough these resist compositions can exhibit good adhesion to thesurface of a substrate such as a semiconductor silicon wafer.Accordingly, it is eagerly desired to develop a method for forming apatterned resist layer capable of exhibiting excellent adhesion to thesubstrate surface even when the substrate has a metallic surface.

Various proposals and attempts have been made in order to improveadhesion between a photoresist layer and a substrate surface. Forexample, Japanese Patent Kokai 62-180357 teaches admixture of aphotopolymerizable monomeric composition with a benzimidazole compoundas an adhesion improver. Although this method is effective when thesubstrate is a silicon wafer, no particular improvement can be obtainedin the adhesion of the resist layer when the substrate has a metallicsurface or, in particular, surface of tantalum.

SUMMARY OF THE INVENTION

The present invention accordingly has an object to provide a novelmethod for forming a patterned resist layer capable of exhibitingexcellent adhesion to the substrate surface even when the substrate hasa metallic surface of, for example, tantalum.

The method of the present invention for forming a patterned resist layeron a metallic substrate surface of tantalum comprises the steps of:

(A) coating the substrate surface with a positive-working photosensitiveresin composition comprising, as a uniform blend,

(a) an alkali-soluble novolac resin;

(b) a quinone diazide group-containing organic compound; and

(c) a polyhydroxy aromatic compound having two benzene rings in amolecule selected from the group consisting of (c-1) the compoundsrepresented by the general formula ##STR1## in which R¹ to R¹⁰ are each,independently from the others, a hydrogen atom, alkyl group having 1 to4 carbon atoms, alkenyl group, halogen atom, hydroxy group, alkoxy groupor carboxyl group including at least five hydroxy groups and X is adivalent atom or group of the formula --CO--O--, --CO--, --S--, --SO--,--SO₂ --, --O--or --CR₂ --, each R being an alkyl group, (c-2) acompound expressed by the structural formula ##STR2## and (c-3) acompound expressed by the structural formula ##STR3## to form a resistlayer; (B) exposing the resist layer pattern-wise to actinic rays toform a latent image in the resist layer; and

(C) developing the latent image in the resist layer with an aqueousalkaline solution.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

As is described above, the most characteristic feature in the inventivemethod for forming a patterned resist layer on a metallic substratesurface consists in the use of the very specific positive-workingalkali-soluble photosensitive resin composition comprising thecomponents (a), (b) and (c), of which the component (a) is afilm-forming ingredient, the component (b) serves as a photosensitizerand the component (c) serves to improve the adhesion between the resistlayer and the metallic substrate surface. Such a photosensitive resincomposition, of which the component (c) is a compound belonging to theclass (c-1), is not new and disclosed in Japanese Patent Kokai 64-44439teaching that the composition can give a resist layer having improvedphotosensitivity and developability on a semiconductor silicon waferalthough no particular examples are given for the use of a polyhydroxyaromatic compound as the component (c) having more than two phenolichydroxy groups in a molecule.

The component (a) in the photosensitive resin composition used in theinventive method is an alkali-soluble novolac resin which serves as afilm-forming ingredient. The novolac resin is not particularlylimitative and can be freely selected from the alkali-soluble novolacresins conventionally used as a film-forming ingredient inpositive-working photoresist compositions in the prior art. Such analkali-soluble novolac resin is prepared by the condensation reaction ofa phenolic compound such as phenol, cresol, xylenol and the like and analdehyde compound such as formaldehyde in the presence of an acidiccatalyst.

The component (b) in the positive-working photosensitive resincomposition used in the inventive method is a quinone diazidegroup-containing compound which serves as a photosensitizing ingredient.Examples of preferable quinone diazide group-containing compoundsinclude full or partial esterification products of a polyhydroxybenzophenone such as 2,3,4-trihydroxy benzophenone,2,3,4,4'-tetrahydroxy benzophenone and the like andnaphtoquinone-1,2-diazide 5- or 4-sulfonic acid. Other quinonediazidegroup-containing compounds suitable as the component (b) in thecomposition used in the inventive method include orthobenzoquinonediazide, orthonaphtoquinone diazide, orthoanthraquinone diazide,sulfonic acid esters of orthobenzoquinone diazide, orthonaphthoquinonediazide, orthoanthraquinone diazide and the like and reaction productsof orthoquinone diazide sulfonyl chloride and a compound having ahydroxy or amino group such as phenol, 4-methoxy phenol, dimethylphenol, hydroquinone, bisphenol A, naphthol, pyrocatechol, pyrogallol,pyrogallol monomethyl ether, pyrogallol 1,3-dimethyl ether, gallic acid,partially esterified or etherified gallic acid, aniline, 4-aminodiphenyl amine and the like. These compounds can be used either singlyor as a combination of two kinds or more according to need as thecomponent (b) in the photosensitive composition.

Typically, the quinone diazide group-containing compound can be preparedby the condensation reaction of the above mentioned polyhydroxybenzophenone compound with naphthoquinone diazide 5- or 4-sulfonylchloride in a suitable solvent such as dioxane and the like in thepresence of a basic compound as an acid acceptor such as triethanolamine, triethyl amine, alkali carbonates, alkali hydrogen carbonates andthe like to give a full or partial esterification product.

The most characteristic ingredient in the photosensitive resincomposition used in the inventive method is the component (c) which isan aromatic compound having two benzene rings in a molecule and havingat least five phenolic hydroxy groups. Such an aromatic compound isselected from the group consisting of the compounds belonging to theclasses of (c-1), (c-2) and (c-3) defined above. The aromatic compoundbelonging to the class (c-1) is represented by the general formula##STR4## in which R¹ to R¹⁰ are each, independently from the others, ahydrogen atom, alkyl group having 1 to 4 carbon atoms, alkenyl group,halogen atom, hydroxy group, alkoxy group or carboxyl group including atleast five hydroxy groups and X is a divalent atom or group of theformula --CO--O--, --CO--, --S--, --SO--, --SO₂ --, --O--and --CR₂ --,each R being an alkyl group. The compounds belonging to the classes(c-2) and (c-3) are expressed by the structural formulas ##STR5##respectively.

Particular examples of the aromatic compounds represented by the abovegiven general formula (I) include: 2,2',3,4,4'-, 2',3,4,5,6'-,2',3,4,4',5-, 2',3,3',4,5,-, 3,3',4,4',5-, 2',3,4,5,5'- and2',3,4,4',5'-pentahydroxy benzophenones, 2',3,4,4',5'-pentahydroxy-3'-,2',3,4,5,6'-pentahydroxy-4'-, 2',3,4,4',5-pentahydroxy-6'-,2',3,3',4,5-pentahydroxy-6'-, 2',3,3',4,5-pentahydroxy-5'- and3,3',4,4',5-pentahydroxy-6'-methylbenzophenones, 2,2',3,4,4',5'-,2',3,3',4,5,6'-, 2',3,4,4',5,5'-, 2',3,4,4',5,6'- and2',3,3',4,4',5-hexahydroxy benzophenones, 2-(2,3,4-trihydroxyphenyl)-2-(2',4'-dihydroxyphenyl) propane,2-(2,3,4-trihydroxyphenyl)-2-(2',4',5'-trihydroxyphenyl) propane,2-(2,3,4-trihydroxyphenyl) -2-(2',3',4'-trihydroxyphenyl) propane,2,2',3,4,4'-phentahydroxy and 2,2',3,4,4',5'-hexahydroxydiphenylsulfides, 2,2',3,3',4,4'-hexahydroxyphenyl benzoate, 2,2',3,4,4'-pentahydroxy diphenylsulfoxide, 2',3,4,5,6'-pentahydroxydiphenylsulfone, 2',3,3',4,5-pentahydroxy diphenyl ether and the like.These aromatic compounds as the component (c), which serve to improvethe adhesion between the patterned photoresist layer and the surface ofa metallic substrate, can be used either singly or as a combination oftwo kinds or more according to need.

The weight proportion of the alkali-soluble novolac resin as thecomponent (a) and the quinone diazide group-containing compound as thecomponent (b) in the photosensitive resin composition should be suchthat the amount of the component (a) is in the range from 5 to 200 partsby weight or, preferably, from 10 to 60 parts by weight per 10 parts byweight of the component (b). When the amount of the novolac resin is toolarge, the fidelity of image transfer would be poor along with adecrease in the transferability. When the amount of the novolac resin istoo small, on the other hand, the resist layer formed from thecomposition would be poor in the uniformity and the resolution ofpatterning would also be decreased.

The amount of the polyhydroxy aromatic compound as the component (c) inthe inventive composition is in the range from 0.5 to 50 parts by weightor, preferably, from 1.0 to 40 parts by weight per 100 parts by weightof the total amount of the components (a) and (b). When the amount ofthe component (c) is too small, the desired effect of improvement of theadhesion between the patterned resist layer and the metallic substratesurface cannot be fully exhibited as a matter of course. On the otherhand, the desired effect by the addition of this component cannot befurther increased even by increasing the amount thereof to exceed theabove mentioned upper limit rather with an undesirable influence thatthe sensitivity of the photosensitive resin composition is somewhatdecreased. The optimum amount of the component (c) depends on the typeof the photosensitizing ingredient.

It is optional that the photosensitive resin composition used in themethod of the invention is admixed according to need with various kindsof known additives conventionally used in photosensitive resincompositions having compatibility with the essential ingredients of thecomposition. Examples of such optional additives include auxiliaryresins, plasticizers and stabilizers to improve the properties of theresist layer, coloring agents to improve the visibility of the patternedresist layer formed by development, additional photosensitizers tofurther enhance the sensitivity of the composition, and so on.

The alkali-soluble, positive-working photosensitive resin compositionused in the inventive method can be prepared by dissolving the abovedescribed essential components (a), (b) and (c) and optional ingredientseach in a specified amount in a suitable organic solvent to form auniform solution which is, in step (A) of the inventive method, appliedto the surface of a metallic substrate such as a vapor-deposited film oftantalum on a glass plate by using a spinner or other suitable coatingmachines followed by drying to give a uniform resist layer.

Examples of suitable organic solvents for the purpose include ketonessuch as acetone, methyl ethyl ketone, cyclohexanone, methyl isoamylketone, methyl tert-butyl ketone and the like, polyhydric alcohols andderivative thereof such as monomethyl, monoethyl, monopropyl, monobutyland monophenyl ethers of ethyleneglycol, ethyleneglycol monoacetate,diethyleneglycol or diethyleneglycol monoacetate and the like, cyclicethers such as dioxane and the like and esters such as ethyl lactate,methyl acetate, ethyl acetate, butyl acetate, methyl pyruvate, ethylpyruvate, ethyl 3-ethoxy propionate and the like. These organic solventscan be used either singly or as a mixture of two kinds or more accordingto need.

In step (B) of the inventive method, the resist layer formed on thesurface of a metallic substrate by using the photosensitive resincomposition is exposed pattern-wise through a pattern-bearing photomaskwith actinic rays such as ultraviolet light emitted from a low-pressuremercury lamp, high-pressure mercury lamp, ultrahigh-pressure mercurylamp, arc lamp, xenon lamp and the like to form a latent image of thepattern therein. Alternatively, the resist layer can be irradiatedpattern-wise by scanning with electron beams. The thus formed latentimage of the pattern can be developed, in step (C) of the inventivemethod, by using an alkaline developer solution such as an aqueoussolution of tetramethyl ammonium hydroxide in a concentration of 1 to10% by weight so that the resist layer on the areas pattern-wise exposedto actinic rays, which is imparted with increased solubility in thedeveloper solution, is selectively dissolved away leaving the resistlayer on the unexposed areas to form a patterned resist layer which is ahigh-fidelity reproduction of the pattern on the photomask. Thereafter,the surface of the metallic substrate pattern-wise exposed bare by theremoval of the resist layer is subjected to etching or other necessarytreatment with the patterned resist layer as the masking followed byremoval of the patterned resist layer.

In the following, the method of the invention using the specificphotosensitive resin composition is described in more detail by way ofexamples, which, however, never limit the scope of the present inventionin any way. In the following examples, the patterned resist layersformed from the respective photosensitive resin compositions wereevaluated for the adhesion between the patterned resist layer and thesurface of the metallic substrate on which the resist layer was formedby the procedure described in Example 1. The results obtained by theelectron microscopic examination of the line-wise patterned resist layerwere rated in three ratings of A, B and C relative to the minimum widthof the line-formed resist layer which was found to work satisfactorilyas an etching resist of the tantalum film as the substrate according tothe criteria of: A for a minimum width of 2 μm or smaller; B for aminimum width larger than 2 μm but not exceeding 10 μm; and C for aminimum width exceeding 10 μm. The photosensitive resin composition canbe used satisfactorily in practical applications when this minimum widthof the line pattern is 10 μm or smaller. In other words, the procedureusing the photosensitive resin compositions is within the scope of theinvention when they are rated in A or B in the above mentioned criteriafor the adhesion test.

Example 1

A positive-working photosensitive resin composition in the form of auniform solution was prepared by dissolving, in 400 g of ethyleneglycolmonoethyl ether acetate, 100 g of a cresol novolac resin having aweight-average molecular weight of about 12,000 as prepared by aconventional method from a 6:4 mixture of m- and p-cresols, 30 g of anaphthoquinone-1,2-diazide-5-sulfonic acid ester of2,3,4,4'-tetrahydroxy benzophenone and 10 g of 2,2',3,4,4'-pentahydroxybenzophenone.

The photosensitive resin solution thus prepared was applied by using aspinner to the surface of a tantalum film vapor-deposited on a glassplate as the substrate in a coating thickness of 1.75 μm as dried toform a uniform resist layer which was subjected to a pre-bakingtreatment on a hot plate at 110° C. for 90 seconds and then exposedpattern-wise to ultraviolet light through a test pattern photomask on acontact-exposure machine (Model PLA-500F manufactured by Canon Co.). Thethus pattern-wise exposed resist layer on the substrate was immersed ina 2.5% by weight aqueous solution of tetramethyl ammonium hydroxide at23° C. for 100 seconds so that the resist layer on the exposed areas wasdissolved away followed by a baking treatment on a hot plate at 180° C.for 5 minutes to form a line-wise patterned resist layer on the tantalumsurface. The plate was then immersed in an etching solution which was amixed solution of hydrofluoric and nitric acids (SA High-Purity BufferedHydrofluoric Acid, a product by Hashimoto Kasei Co.) at 23° C. for 9minutes to remove the tantalum film on the exposed areas with thepatterned resist layer as the etching resist.

The patterned resist layer was evaluated for the adhesion with thetantalum surface below by the electron microscopic examination to findthat the minimum width of the line-formed resist layer which workedsatisfactorily as the masking was 1 μm to show excellent performance ofthe resin composition.

EXAMPLE 2 to 17 AND COMPARATIVE EXAMPLES 1 to 7

The experimental procedure in each of these examples and comparativeexamples was substantially the same as in Example 1 except that the2,2',3,4,4'-pentahydroxy benzophenone used in Example 1 was replacedwith the compound indicated in Table 1 in an amount also indicated inthe same table. The experiment in Comparative Example 7 was carried outby merely omitting the 2,2',3,4,4'-pentahydroxy benzophenone to give aminimum line width of 30 μm. The substitute compounds for2,2',3,4,4'-pentahydroxy benzophenone in Examples 16 and 17 were thecompounds expressed by the structural formulas (II) and (III),respectively, to give the minimum line widths of 2 μm and 1.5 μm,respectively, indicating quite satisfactory adhesion of the resist layerto the substrate surface.

                  TABLE 1                                                         ______________________________________                                                                Amount                                                                        added,   Adhe-                                               Aromatic compound                                                                              g        sion                                         ______________________________________                                        Example                                                                       2        2,2',3,4,4'-Pentahydroxy benzo-                                                                  30       A                                                 phenone                                                              3        2,2',3,4,4'-Pentahydroxy benzo-                                                                  50       B                                                 phenone                                                              4        2,2',3,4,4',5'-Hexahydroxy                                                                       10       A                                                 benzophenone                                                         5        2,2',3,4,4',5'-Hexahydroxy                                                                       30       A                                                 benzophenone                                                         6        2,2',3,4,4',5'-Hexahydroxy                                                                       50       B                                                 benzophenone                                                         7        2-(2,3,4-trihydroxyphenyl)-2-                                                                    10       A                                                 (2',4'-dihydroxyphenyl)                                                       propane                                                              8        2-(2,3,4-trihydroxyphenyl)-2-                                                                    30       A                                                 (2',4'-dihydroxyphenyl)                                                       propane                                                              9        2,2',3,4,4'-Pentahydroxy                                                                         10       A                                                 diphenylsulfide                                                      10       2,2',3,4,4'-Pentahydroxy                                                                         30       A                                                 diphenylsulfide                                                      11       2-(2,3,4-trihydroxyphenyl)-                                                                      10       A                                                 2-(2',4',5'-trihydroxyphenyl)                                                 propane                                                              12       2-(2,3,4-trihydroxyphenyl)-                                                                      30       A                                                 2-(2',4',5'-trihydroxyphenyl)                                                 propane                                                              13       2-(2,3,4-trihydroxyphenyl)-                                                                      10       A                                                 2-(2',3',4'-trihydroxyphenyl)                                                 propane                                                              14       2,2',3,4,4',5'-Hexahydroxy                                                                       10       A                                                 diphenylsulfide                                                      15       2,2',3,4,4',5'-Hexahydroxy                                                                       30       A                                                 diphenylsulfide                                                      16       Compound expressed by struc-                                                                     10       A                                                 tural formula (II)                                                   17       Compound expressed by struc-                                                                     10       A                                                 tural formula (III)                                                  Comparative                                                                   Example                                                                       1        2,3,4-Trihydroxy benzophenone                                                                    10       C                                        2        2-(2,3,4-trihydroxyphenyl)-                                                                      10       C                                                 2-phenyl propane                                                     3        2,3,4-Trihydroxy diphenyl-                                                                       10       C                                                 sulfide                                                              4        2,2',4,4'-Tetrahydroxy benzo-                                                                    10       C                                                 phenone                                                              5        2-(2,4-dihydroxyphenyl)-2-                                                                       10       C                                                 (2',4'-dihydroxyphenyl)                                                       propane                                                              6        2,2',4,4'-Tetrahydroxy                                                                           10       C                                                 diphenylsulfide                                                      ______________________________________                                    

What is claimed is:
 1. A method for forming a patterned resist layer ona substrate, of which at least the surface layer is made from tantalum,which comprises the steps of:(A) coating the substrate surface with apositive-working photosensitive resin composition comprising, as auniform blend,(a) an alkali-soluble novolac resin; (b) a quinone diazidegroup-containing organic compound; and (c) an aromatic compound havingtwo benzene rings in a molecule selected from the group consisting of(c-1) the compounds represented by the general formula ##STR6## in whichR¹ to R¹⁰ are each, independently from the others, a hydrogen atom,alkyl group having 1 to 4 carbon atoms, alkenyl group, halogen atom,hydroxy group, alkoxy group or carboxyl group including at least fivehydroxy groups and X is a divalent atom or group of the formula--CO--O--, --CO--, --S--, --SO--, --SO₂ --, --O-- or --CR₂ --, each Rbeing an alkyl group, (c-2) a compound expressed by the structuralformula ##STR7## and (c-3) a compound expressed by the structuralformula ##STR8## to form a resist layer; (B) exposing the resist layerpattern-wise to actinic rays to form a latent image in the resist layer;and (C) developing the latent image in the resist layer by treating saidlayer with an aqueous solution to remove the imagewise exposed areas. 2.The method for forming a patterned resist layer on a substrate, of whichat least the surface layer is made from tantalum, as claimed in claim 1in which the amount of the component (a) in the photosensitive resincomposition is in the range from 5 to 200 parts by weight per 10 partsby weight of the component (b).
 3. The method for forming a patternedresist layer on a substrate, of which at least the surface layer is madefrom tantalum, as claimed in claim 2 in which the amount of thecomponent (a) in the photosensitive resin composition is in the rangefrom 10 to 60 parts by weight per 10 parts by weight of the component(b).
 4. The method for forming a patterned resist layer on a substrate,of which at least the surface layer is made from tantalum, as claimed inclaim 1 in which the amount of the component (c) in the photosensitiveresin composition is in the range from 0.5 to 50 parts by weight per 100parts by weight of the total amount of the components (a) and (b). 5.The method for forming a patterned resist layer on a substrate, of whichat least the surface layer is made from tantalum, as claimed in claim 4in which the amount of the component (c) in the photosensitive resincomposition is in the range from 1.0 to 40 parts by weight per 100 partsby weight of the total amount of the components (a) and (b).
 6. Themethod for forming a patterned resist layer on a substrate, of which atleast the surface layer is made from tantalum, as claimed in claim 1 inwhich the component (c) is a compound belonging to the class (c-1)selected from the group consisting of 2,2',3,4,4'-, 2',3,4,5,6'-,2',3,4,4',5-, 2',3,3',4,5,-, 3,3',4,4',5-, 2',3,4,5,5'- and2',3,4,4',5'-pentahydroxy benzophenones.
 7. The method for forming apatterned resist layer on a substrate, of which at least the surfacelayer is made from tantalum, as claimed in claim 1 in which thecomponent (c) is a compound belonging to the class (c-1) selected fromthe group consisting of 2',3,4,4',5'-pentahydroxy-3'-,2',3,4,5,6'-pentahydroxy-4'-, 2',3,4,4',5-pentahydroxy-6'-,2',3,3',4,5-pentahydroxy-6'-, 2',3,3',4,5-pentahydroxy-5'-and3,3',4,4',5-pentahydroxy-6'-methylbenzophenones.
 8. The method forforming a patterned resist layer on a substrate, of which at least thesurface layer is made from tantalum, as claimed in claim 1 in which thecomponent (c) is a compound belonging to the class (c-1) selected fromthe group consisting of 2,2',3,4,4',5'-, 2',3,3',4,5,6'-,2',3,4,4',5,5'-, 2',3,4,4',5,6'- and 2',3,3',4,4',5-hexahydroxybenzophenones.
 9. The method for forming a patterned resist layer on asubstrate, of which at least the surface layer is made from tantalum, asclaimed in claim 1 in which the component (c) is a compound belonging tothe class (c-1) selected from the group consisting of2-(2,3,4-trihydroxyphenyl)-2-(2',4'-dihydroxyphenyl) propane,2-(2,3,4-trihydroxyphenyl)-2(2',4',5'-trihydroxyphenyl) propane,2-(2,3,4-trihydroxyphenyl)-2-(2',3',4'-trihydroxyphenyl) propane and2,2',3,4,4'-phentahydroxy and 2,2',3,4,4',5'-hexahydroxydiphenylsulfides.
 10. The method for forming a patterned resist layer ona substrate, of which at least the surface layer is made from tantalum,as claimed in claim 1 in which the component (b) is a compound selectedfrom the group consisting of full or partial esterification products of2,3,4-trihydroxy benzophenone, 2,3,4,4'-tetrahydroxy benzophenone andnaphtoquinone-1,2-diazide 5- or 4-sulfonic acid.
 11. The method forforming a patterned resist layer on a substrate, of which at least thesurface layer is made from tantalum, as claimed in claim 1 in which thecomponent (c) is a compound belonging to the class (c-2).
 12. The methodfor forming a patterned resist layer on a substrate, of which at leastthe surface layer is made from tantalum, as claimed in claim 1 in whichthe component (c) is a compound belonging to the class (c-3).